The purpose of this study was to analyze the type and frequency of defects in nickel-titanium rotary endodontic files after routine clinical use, and to draw conclusions regarding the reasons for ...failure. All of the files (total: 378, Quantec Series 2000) discarded after normal use from a specialist endodontic practice over 6 months were analyzed. Almost 50% of the files showed some visible defect; 21% were fractured and 28% showed other defects without fracture. Fractured files could be divided into two groups according to the characteristics of the defects observed. Torsional fracture occurred in 55.7% of all fractured files, whereas flexural fatigue occurred in 44.3%. The results indicated that torsional failure, which may be caused by using too much apical force during instrumentation, occurred more frequently than flexural fatigue, which may result from use in curved canals.
Abstract Dentinal tubules occupy a substantial proportion of total dentin volume, especially of inner dentin. Resin-based sealer cements are known to penetrate deeply into dentinal tubules, but their ...ability to influence root strength is controversial. In this study, the contribution of dentinal tubules to shear strength and the influence of a resin-based sealer on shear strength were evaluated. Coronal 100-μm sections of 12 single-canal premolar teeth were tested in different locations (buccal and proximal) and tubule directions (parallel and perpendicular) using the micropunch shear test (MPSS). Tests were also conducted by using 10 two-canal premolars, with one untreated canal and the other obturated using epoxy resin-based sealer (plus gutta-percha). No difference in MPSS was found because of location or tubule orientation (p > 0.05). Outer dentin had a higher MPSS than middle and inner dentin (p < 0.001). Tubule infiltration by epoxy resin did not increase MPSS.
Milk caseins stabilize calcium and phosphate ions and make them available to the neonate. Tryptic digestion of the caseins yields phosphopeptides from their polar N-terminal regions that contain ...clusters of phosphorylated seryl residues. These phosphoseryl clusters have been hypothesized to be responsible for the interaction between the caseins and calcium phosphate that lead to the formation of casein micelles. The casein phosphopeptides stabilize calcium and phosphate ions through the formation of complexes. The calcium phosphate in these complexes is biologically available for intestinal absorption and remineralization of subsurface lesions in tooth enamel. We have studied the structure of the complexes formed by the casein phosphopeptides with calcium phosphate using a range of physicochemical techniques including x-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and equilibrium binding analyses. The amorphous nature of the calcium phosphate phase was confirmed by two independent methods: x-ray powder diffraction and selected area diffraction. In solution, the ion activity product of a basic amorphous calcium phosphate phase was the only ion product that was a function of bound phosphate independent of pH, consistent with basic amorphous calcium phosphate being the phase stabilized by the casein phosphopeptides. Detailed investigations of calcium and calcium phosphate binding using a library of synthetic homologues and analogues of the casein phosphopeptides have revealed that although the fully phosphorylated seryl-cluster motif is pivotal for the interaction with calcium and phosphate, other factors are also important. In particular, calcium binding and calcium phosphate stabilization by the peptides was influenced by peptide net charge, length, and sequence.
Objective
The aim of this laboratory study was to investigate the effect of three commercial bleaching agents and Tooth Mousse™ containing 10% w/w casein phosphopeptide–amorphous calcium phosphate on ...the hardness of tooth enamel.
Methods
Sixteen human enamel specimens were exposed to one of three commercial bleaching agents with or without subsequent exposure to Tooth Mousse™. Nanoindentation was used to measure the hardness and reduced modulus before and after treatments.
Results
When bleaching materials were applied for a short period of time following the manufacturers' instructions, there was an increase in enamel hardness and reduced modulus for some bleaching groups, with no statistically significant difference from the baseline values. After extended bleaching periods a statistically significant decrease in enamel hardness and reduced modulus was found and after applying Tooth Mousse™ post‐bleaching, the hardness and reduced modulus returned to close to baseline values.
Conclusion
The application of bleaching agents for an extended period of time significantly decreases enamel hardness and the reduced modulus. The application of Tooth Mousse™ after bleaching was able to reestablish the baseline enamel hardness and reduced modulus, decreasing the adverse effects of bleaching enamel.
The purpose of this work was to investigate fluid flow after restoration using four restorative procedures. Micro‐gap, internal dye leakage, and micropermeability of bonded interfaces were also ...investigated. Each tooth was mounted, connected to a fluid flow‐measuring device, and an occlusal cavity was prepared. Fluid flow after cavity preparation was recorded as the baseline measurement, and the cavity was restored using one of four restorative procedures: bonding with total‐etch (Single Bond 2) or self‐etch (Clearfil SE Bond) adhesives without lining; or lining with resin‐modified glass‐ionomer cement (GIC) (Fuji Lining LC) or conventional GIC (Fuji IX) and then bonding with the total‐etch adhesive. Fluid flow was recorded after restoration and at specific time‐points up to 6 months thereafter and recorded as a percentage. Micro‐gap formation was analyzed using resin replicas and scanning electron microscopy. Internal leakage of 2% methylene blue dye was observed under a light microscope. In micro‐permeability testing, fluorescent‐dye penetration was investigated using confocal laser microscopy. None of the restorative procedures provided a perfectly sealed restoration. Glass‐ionomer lining did not reduce fluid flow after restoration, and micro‐gaps were frequently detected. The self‐etch adhesive failed to provide a better seal than the total‐etch adhesive, and even initial gap formation was rarely observed for the former. Penetration of methylene blue and fluorescent dyes was detected in most restorations.
Background
Lengthening of soft-tissue contractures is frequently required in children with a wide variety of congenital and acquired deformities. However, little is known about the biomechanics of ...surgical procedures which are commonly used in contracture surgery, or if variations in technique may have a bearing on surgical outcomes. We investigated the hypothesis that the site of intramuscular tenotomy (IMT) within the muscle–tendon-unit (MTU) of the tibialis posterior (TP) would affect the lengthening characteristics.
Methods
We performed a randomized trial on paired cadaver tibialis posterior muscle–tendon-units (TP-MTUs). By random allocation, one of each pair of formalin-preserved TP-MTUs received a high IMT, and the other a low IMT. These were individually tensile-tested with an Instron® machine under controlled conditions. A graph of load (Newtons) versus displacement (millimetres) was generated for each pair of tests. The differences in lengthening and load at failure for each pair of TP-MTUs were noted and compared using paired t tests.
Results
We found 48% greater lengthening for low IMT compared to high IMT for a given load (P = 0.004, two tailed t test). Load at failure was also significantly lower for the low IMT. These findings confirm our hypothesis that the site of the tenotomy affects the amount of lengthening achieved. This may contribute to the reported variability in clinical outcome.
Conclusions
Understanding the relationship between tenotomy site and lengthening may allow surgeons to vary the site of the tenotomy in order to achieve pre-determined surgical goals. It may be possible to control the surgical “dose” by altering the position of the intramuscular tenotomy within the muscle–tendon-unit.
Evaluation of the fit of CAD/CAM abutments Hamilton, Adam; Judge, Roy B; Palamara, Joseph E ...
The International journal of prosthodontics,
07/2013, Volume:
26, Issue:
4
Journal Article
Peer reviewed
This study aimed to compare the fit of computer-aided design/computerassisted manufacture (CAD/CAM) abutments provided by a single system with proprietary prefabricated abutments on various implant ...systems.
Titanium CAD/CAM abutments were compared with prefabricated abutments on five different implant types. The samples were embedded in epoxy resin, sectioned longitudinally, and polished. Scanning electron microscopy was used to measure the gap between the implants and abutments at the connecting flanges and internal features. Independent t tests were used to compare data.
A mean difference of 1.86 μm between the gold synOcta and CAD/CAM abutments on the Straumann Standard Plus implant was observed to be statistically significant (P = .002). Less than 0.4 μm of difference was found between the CAD/CAM and prefabricated abutments for the remaining implant types, and statistical significance was not observed. Mean differences of 34.4 μm (gold) and 44.7 μm (titanium) were observed between the CAD/ CAM and prefabricated abutments on the Straumann Standard Plus implants, which were statistically significant (P < .001). A mean difference of 15 μm was also observed between the CAD/CAM and prefabricated abutment on the NobelReplace implant, which was statistically significant (P = .026). All other groups had less that 4 μm of difference, and statistical significance was not observed.
The CAD/CAM abutments appeared to have a comparable fit with prefabricated abutments for most of the systems evaluated. Design differences between the abutment connections for both Straumann implants were observed that affected the fit of internal components of the implant-abutment connections.
Objectives: The aim of this study was to investigate the creep, stress relaxation and strain rate behavior of human root dentin under compressive loading.
Methods: Cylindrical root dentin samples of ...3.5
mm outer diameter, 1.5
mm internal canal diameter and 6–10
mm long were prepared from freshly extracted teeth. The samples were tested in a closed-loop servohydraulic testing machine at constant load or displacement, and varied strain rate. In vivo strain rates were estimated using strain gauges bonded to human teeth.
Results: A family of creep curves, determined at different loads within dentin's elastic region, was found to be consistent with a material having linear viscoelastic behavior. A positive correlation (
r
2=0.79,
P<0.001) was found between creep rate and stress. Young's modulus (
E) was found to be a function of the strain rate with rates of loading in the range 10–500,000
Ns
−1. Loading at constant displacement showed stress to be a decreasing function of time (i.e. stress relaxation).
Significance: Dentin showed linear-viscoelastic behavior under various conditions of compressive loading. Time dependent properties of dentin should be taken into account in restorative dentistry.
This experimental study was designed to examine whether screw head design influenced the angle of application of a screwdriver at which failure of engagement or stripping of the screw head occurred.
...Four different screw head designs (slot, cross, square, star) were tested in a custom-made jig that was designed to enable the screws to be tested over a range of angles of application of the respective screwdrivers, to determine whether the screw head design influenced the torque value at which the screw head stripped or failure of driver engagement occurred.
The results fell clearly into 2 groups: The slot and cross designs gave the highest torque values at all angles, while the torque values for the square and star designs dropped to a low value with increasing angulation between the screw and driver. These differences were significant (
P < .001).
Although this experimental situation cannot be entirely extrapolated to the clinical situation, it indicates that the slot or cross design may offer an advantage in regions of difficult access where the angulation of the screwdriver to the screw may of necessity be increased.
Nickel-titanium engine-driven rotary instruments are used increasingly in endodontic practice. One frequently mentioned problem is fracture of an instrument in the root canal. Very few studies have ...been conducted on torsional characteristics of these instruments, and none has been done under dynamic conditions. The purposes of this study were to measure the torque generated and the apical force applied during instrumentation with a commercial engine-driven nickel-titanium file system, and to relate torque generated during simulated clinical use to torsional failure of the instruments. Ten extracted human teeth (five with small-sized and five with medium-sized straight root canals) were instrumented with Quantec Series 2000 files, and the torque and apical force generated were measured. The applied apical force was generally low, not exceeding 150 g in either small or medium canals. The torque depended on the tip size and taper of each instrument, and on canal size. Instruments with 0.05 and 0.06 taper generated the highest torque, which was greater in small than in medium canals. The torque at failure was significantly (p < 0.001) higher than torque during instrumentation, but with considerable variation in the extent of the difference.
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